C Language Interview: Code Debugging and Error Handling

In the software development process, debugging and error handling are crucial steps to ensure code quality. Especially in job interviews, examiners often assess candidates’ understanding of code debugging and error handling to evaluate their capabilities. This article will detail the basic debugging techniques and error handling methods in C language, along with practical code demonstrations to help beginners understand.

1. Basic Debugging Methods in C Language

1. Using Print Statements

The simplest and most commonly used debugging method is to insert printf statements at critical points, allowing observation of variable values and program execution flow. This method is intuitive and suitable for small-scale programs.

#include <stdio.h>
int main() {    int a = 10;    int b = 20;    printf("a: %d, b: %d\n", a, b); // Print variable values
    int sum = a + b;    printf("sum: %d\n", sum); // Print calculation result    return 0;}

2. Using Assertions (assert)

Using the assert macro can check condition expressions; if the condition is false, the program will automatically terminate and output corresponding information, which is helpful for capturing logical errors.

#include <stdio.h>
#include <assert.h>
int main() {    int x = -5;
    assert(x >= 0); // If x is less than 0, the program will terminate and report an error
    printf("x is a positive number: %d\n", x);
    return 0; }

3. Using gdb Debugger

The GNU Debugger (gdb) is a powerful command-line tool for dynamically observing program behavior. We can set breakpoints, step through execution, etc., making it easier to find issues.

Compile Code: Please use gcc -g filename.c -o outputfile to compile with the -g option to generate information for gdb debugging.
Start gdb: Enter gdb ./outputfile
Set Breakpoints: In the source file, enter break line_number
Run Program: Enter run

2. Error Handling in C Language

In C programs, various types of exception checks are often required, such as memory allocation failures, file operation failures, etc. Below are several basic error handling methods.

1. Check Return Values

Many system calls and library functions return status codes to indicate success or failure. For example, after memory allocation, we need to check if it was successful:

#include <stdio.h>
#include <stdlib.h>
int main() {   int *ptr = malloc(sizeof(int) * 10);
   if (ptr == NULL) { // Check if pointer is NULL       fprintf(stderr, "Memory allocation failed\n");       return EXIT_FAILURE;    }
   // Continue operations normally...
   free(ptr); // Don't forget to free memory
   return EXIT_SUCCESS; }

2. errno and perror()

Some standard library functions (such as file operations) set the global variable errno if an error occurs. We can use it to obtain specific error information and use the perror() function to output that information:

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
int main() {   FILE *file = fopen("nonexistent.txt", "r");
   if (!file) {       perror("Failed to open file"); // Output corresponding error information        return EXIT_FAILURE;    }
   fclose(file);
   return EXIT_SUCCESS; }

Conclusion

The above content demonstrates some basic and important debugging and error handling techniques in C language. For beginners, mastering these skills will help in solving problems more smoothly. In actual work or interviews, it can also improve your efficiency and confidence in solving complex issues. In future practice, please practice these methods to enhance your programming skills.